The present invention relates to an endless chain type cutter for excavating a ditch in the ground for use when constructing an underground continuous wall in civil engineering works.
Previously, in order to construct an underground continuous wall, it was necessary to excavate an elliptical hole, 2 or 3 m (6 or 10 feet) wide, down to a predetermined depth from the ground surface, or to drill into the ground with an auger drill with double or triple lanes down to a predetermined depth, and then to insert a reinforcement cage or steel members. Finally, cement was poured into the hole, or ready mixed concrete was cast in the hole. By repeating this process with successive holes intercepting preceding ones, a continuous underground wall could be constructed.
In the prior method for constructing an underground continuous wall described above, there are some problems as follows. Since the machinery for excavating the holes is about 30 m (100 feet) tall, there is a danger that it may fall over. Secondly, the construction process is complicated, so-the construction period is prolonged. Also, a film of muddy water, bentonite or the like is formed where one hole intercepts the preceding section of wall, so a perfect joint cannot be made in order to form a continuous wall. Underground water may leak through the joints after completion of the works. It is therefore difficult to attain simultaneously the objectives of safely and rapidly constructing a wall in the ground which is also perfectly continuous.
Because of these problems, a method of making an underground continuous wall as shown in the schematic views of FIGS. 8 and 9 has been tried. In this method an endless chain type cutter c is disposed on one side of a self-propelled vehicle b having crawler tracks a. A continuous ditch is excavated in the ground by advancing the self-propelled vehicle b in the direction of the arrow A of FIGS. 8 and 9 while driving the cutter c. Then cement or concrete is poured into the ditch.
In the endless chain cutter c mentioned above, an endless chain f is spanned between upper and lower chain sprockets d and e and groups of cutter elements are disposed protrudingly on the outer side of this chain f at predetermined intervals. Within each group of cutter elements, cutter bits g1-g9 are arranged on base plates h, attached to the chain f, for example as shown in FIG. 10.
When the chain cutter having cutter bits g1-g9 as shown in FIG. 10 is advanced in the direction of the arrow A in FIGS. 8, 9 the sprockets d and e are rotated to drive the chain so that the cutter bits move in the upward or downward directions of the drawings. The excavating loci i1-i9 as shown by hatched lines in FIG. 10 are made on the ground in the upright face which is being cut in front of the cutter c. If the ground to be excavated is weak, then it can be efficiently excavated by the above-mentioned excavating loci i1-i9. However, in the case where the ground is hard and strong, there is a problem that the portions j1-j7 (see FIG. 10) of the ground in front of the cutter remain in place. When these remaining portions hit the outer surface of the base plate h or the endless chain f, these meet with increased resistance, so that the continuation of the excavating work is hampered.
The present invention aims to overcome this and other problems.
In the present invention there is provided an endless chain type cutter having an endless chain extending between upper and lower sprockets and at least one group of cutter elements thereon for use in cutting, in the ground, a ditch of pre-determined width, characterised by the cutter elements of each group, together, being arranged to cut the ground throughout the width between the laterally outermost cutter elements of the group.
With the invention, therefore, each group of cutter elements can cut each part of the ground in the width of the ditch being cut, ensuring that the ground is disturbed and loosened throughout the width of the ditch.
Typically, there are about ten elements in a group, and some elements are preferably of bucket type. The number of groups on the chain will depend on its length, but 4 to 8 groups may be typical.
The invention also provides apparatus for excavating a ditch including a vehicle, which is preferably a tracked vehicle, with such an endless chain type cutter mounted thereon.
The invention also provides a method of excavating a ditch using such an endless chain type cutter in which, in a time in which the endless chain moves along its path between the upper and lower sprockets by a distance corresponding to the length of a said group of cutter elements, the endless chain is advanced along the direction of the ditch being cut by a distance which is less than the distance by which the cutter elements project from the chain.
This method ensures that, even if the ground is hard and strong the chain itself will not engage the ground being cut.